I thought this would go well with the "How often do you change your main system?" poll.

*(new disk drives, sound cards, TV cards, and the like)

**(everything but new motherboards and CPUs)

cooling replacement is of course excluded(including for the first option)

I've only been upgrading during my whole PC "career". I don't do so often, however, and never go top-of-the-line; instead, most of my components are mid-range due to budget limits. Lately, my upgrades have obviously been for silence, but they also yield substantial performance benefits as well, such as improvements in hard drive speed, case airflow, and PSU efficiency.